It could just be that you need to give the spells time, but you should also trust in your spells. You can't just do them and think it will work. You have to believe it will work. It all depends on your energy that you are putting into your spell. I hope this helps.

That and learning the basics help. You need to build a solid foundation. Want to cast spells? Do you know how they work? Why they work? How to create your own? Ask yourself these questions. Basics, basics, basics.

First, ask yourself why you need to cast a spell? Do you really need a spell for a certain purpose where natural means aren't possible, or just to see if they work.
If the purpose is truly valid, then know the spell will work, not just believe.
From a book I once read(can't remember the name), it states,
To believe is to have doubts.
To know is to perceive directly from the senses and mind.
And study up upon the Hermatic Quatranary...To Know,To Will,To Dare...and To keep Silent. Basically the four sides of magic.
Hope this helps,
Peace